The 21-year-old stretched his run of consecutive set wins to 18 with his 6-4 6-4 success, which follows on from his triumph on clay at the BMW Open in Munich last week.
Thiem had stunned the seemingly unstoppable Rafael Nadal in the quarter-finals but could not repeat the feat against Zverev.
Zverev won the title with a thrillingly aggressive performance, breaking Thiem in his opening service game and not giving the Austrian any chance of a break back as he took the first set.
Zverev continued to serve so strongly that another break on Thiem’s first service game of the second set always looked likely to prove decisive.
Thiem was forced to save two more break points and Zverev – who did not face a single break point on his own serve – served out to take the title in style.
✅ Sin ceder un set
✅ Sin perder un saque
— Mutua Madrid Open (@MutuaMadridOpen) May 13, 2018
Victory makes Zverev only the fifth player, after the so-called ‘big four’ of Nadal, Roger Federer, Novak Djokovic and Andy Murray, to win three career ATP Masters 1000 titles.
Triple Grand Slam champion Stan Wawrinka struggled on his return from a knee injury as he was beaten 6-4 6-4 by American Steve Johnson in the first round of the Rome Masters.
The 33-year-old has missed three months following a knee operation and his defeat to world number 55 Johnson underlined the work he still needs to do to get back the top of the sport.
Twelfth seed Sam Querrey was upset 6-2 7-6 (9/7) by Germany’s Peter Gojowczyk while other first-round winners were Ryan Harrison, Jack Sock and Italian wild card Lorenzo Sonego.
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